This invention relates to transformer and control units for ac (alternating current) control.
There is a variety of known units which can be plugged into a conventional ac outlet to provide a source of controlled or modified power to a device connected thereto. Among these units are time switches, lamp dimmers, PLC (power line carrier) units which for example operate in accordance with the X-10 protocol, and transformer units which provide a relatively low voltage ac or dc supply for numerous types of electronic device. These units may be in the form of wall units with prongs which plug directly into an ac outlet, or in the form of floor or desk units with a supply cable having a plug which is plugged into an ac outlet. The term xe2x80x9cpluggedxe2x80x9d as used herein is intended to embrace all forms of electrical connection to ac outlets, including for example screw-threaded and bayonet connections typically provided for lamps. The term xe2x80x9cac outletxe2x80x9d as used herein is intended to embrace both grounded (e.g. two-pin) and ungrounded (e.g. three-pin) outlets of any form, and includes an ac outlet provided at the end of a connection cable. The term xe2x80x9ctransformer unitxe2x80x9d as used herein is intended to embrace both wall transformer units and floor or desk transformer units.
A time switch provides timed control for supply of ac power to an ac outlet on the time switch, or to an ac power output cable of the time switch. A lamp dimmer similarly provides controlled power to an ac outlet on the lamp dimmer unit or to a power output cable to which a lamp can be connected. The lamp dimmer provides for example a manual control of the conduction phase angle of a triac during each half cycle of the ac waveform, thereby controlling the brightness of the lamp. PLC units provide similar functions but can be remotely controlled, by commands sent by a PLC control unit via the ac power supply lines, to provide timed control and/or dimming control functions.
An X-10 PLC control unit (Radio Shack Home Control Center Computer Interface, Catalog No. 61-2417) is known which has prongs to plug it into an ac outlet, an ac outlet which is directly connected to the prongs, and a modular telephone cord connector providing an interface for connection to a computer. Within this unit, a transformer is connected to the prongs to supply low voltage power to PLC circuits of the unit. Software running on a connected computer enables PLC commands, including commands for timing and dimming functions, to be downloaded to the control unit, which subsequently sends these commands via the ac power lines without requiring continued connection or operation of the computer.
Transformer units which provide relatively low voltage supplies for electronic devices include numerous units for providing various individual or combinations of ac, unregulated dc, or regulated dc voltages at various currents and via various types of connector.
Every day, millions of people are awakened from sleep by a sudden noise, loud enough to wake the sleeper, from an alarm clock, clock radio, or similar device. It has been recognized that such a disruptive start to each day is undesirable, and that a more natural waking environment can be provided by a gradual increase in light, simulating dawn. Accordingly, various dawn/dusk simulators are known and for example are available from The SunBox(copyright) Co. (www.sunboxco.com) of Gaithersburg, Md. These units combine an analog or digital clock with a lamp, or an ac outlet for a lamp, whose brightness is controlled, the lamp being brightened at a desired time to simulate dawn or being dimmed at another desired time to simulate dusk. One of these units further provides sounds that get louder through a simulated dawn and quieter through a simulated dusk, as well as a conventional alarm sound. A disadvantage of such units is their relatively high cost, which makes them impractical for the vast majority of people, especially if such a unit is to be provided in each bedroom of a residence.
It is desirable, therefore, to provide a dawn simulator at a relatively low cost.
It can be appreciated that a dawn simulator comprises a timer, an automatically controlled lamp dimmer, and a lamp. Timers in the form of 24-hour time switches as discussed above are readily available at very low cost, and bedside plug-in lamps already exist in most bedrooms or are also easily provided. However, providing an automatically controlled lamp dimmer at low cost presents a more significant difficulty. For simulating dawn and waking a sleeper naturally, it is preferable for a lamp to be relatively close to the sleeper to provide an ultimately bright source of light, and it is necessary for the lamp to be turned on initially at a very low light level, and to be brightened smoothly over a period of time. Most common lamp dimmers do not allow a lamp to be turned on initially at a very dim level, and are not automatically controlled.
Using a PLC lamp module and a series of successive PLC commands over a period of time, it is possible to brighten a lamp from a dim level to a full brightness level in, for example, 16 brightness steps. However, the most commonly available PLC lamp modules do not permit the lamp to be initially turned on at anything other than its full brightness level, which is as disruptive to a sleeper as the sudden sound of an alarm clock. Although PLC lamp modules exist which obviate this problem, they are less readily available and are more costly. In any event, this solution also requires a PLC control unit, for example as discussed above, to issue the required series of PLC commands, as well as a computer from which to download the series of commands to the PLC control unit and the knowledge to set up, operate, and maintain this.
A need exists, therefore, for an effective dawn simulator that can be provided at low cost, and that does not require relatively sophisticated equipment and knowledge for its proper operation.
It is known that a low-cost microcontroller can be used to provide a lamp dimmer. For example, xe2x80x9cPICDIM Lamp Dimmer for the PIC12C508xe2x80x9d, having a copyright date of 1997 and available from the web site (www.microchip.com) of Microchip Technology Inc. of Chandler, Ariz., where it is identified as PICREF-4, describes the use of a PlCmicro(copyright) 8-bit microcontroller to provide zero crossing detection of an ac waveform and control of the conduction phase angle of a triac to provide manually controlled lamp dimming. Other documents on the same web site provide extensive further information on such microcontrollers and their applications, including for timing functions.
Microcontroller circuits typically have very small power requirements which are often met by using a transformerless ac power supply, an example of which is a capacitive power supply of the type shown in the PICREF-4 document. That document properly draws prominent attention to potential hazards of transformerless power supplies, namely that they present a potential risk because (especially with incorrect ac supply wiring or a malfunction) any part of the connected circuit may be at an ac supply voltage, and there is no transformer isolation for transients between the ac supply and the powered circuit. These potential hazards become of increasing significance in a lamp dimmer with manual switches which may be operated by a person who is not fully awake, and where transients are likely to be produced by the switching of the triac in each half cycle of the ac waveform. Although other protection measures are known for transformerless power supplies, these add complexity without fully avoiding all of the potential hazards. Thus the isolation advantages of a transformer power supply over-ride its disadvantages of bulk and cost, these disadvantages being of relatively low consequence in view of the low power requirements of a microcontroller.
The invention is concerned with addressing the need discussed above in a manner that facilitates providing a safe, versatile, practical, and economic solution.
According to one aspect, this invention provides a transformer unit comprising: a first connector for connection to an ac outlet to provide an ac supply to the transformer unit; a second connector constituting an ac outlet of the transformer unit; a triac, the first connector being coupled to the second connector via the triac to provide a controlled ac supply to the second connector; an electrically isolating coupler for coupling a control signal to the triac for controlling conduction of the triac; a transformer having primary and secondary windings, the primary winding being coupled to the first connector for receiving the ac supply; and a third connector comprising at least three wires for connection to a control unit separate from the transformer unit, said at least three wires providing said control signal from the control unit, a low voltage supply for the control unit derived from the secondary winding of the transformer, and an indication of the timing of a waveform of the ac supply.
In one form of the transformer unit, two of said at least three wires are coupled to the secondary winding of the transformer to provide an ac voltage constituting the low voltage supply for the control unit and the indication of the timing of the waveform of the ac supply. Another form of the transformer unit includes a rectifier, the secondary winding of the transformer being coupled to two of said at least three wires via the rectifier to provide a full wave rectified ac voltage constituting the low voltage supply for the control unit and the indication of the timing of the waveform of the ac supply.
A further form of the transformer unit includes a zero crossing detector arranged to provide a zero crossing signal representing zero crossings of the waveform of the ac supply and constituting said indication of the timing of the waveform of the ac supply. In this case conveniently the transformer unit can include a rectifier and smoothing circuit, the third connector comprising four wires and the secondary winding of the transformer being coupled to two of said four wires via the rectifier and smoothing circuit to provide a dc voltage constituting the low voltage supply for the control unit.
The invention also provides a control unit for connection to a transformer unit as recited above via the third connector of the transformer unit for providing said control signal to control a conduction phase angle of the triac in successive half cycles of the waveform of the ac supply, the control unit comprising a connector having at least three wires for coupling to the third connector of the transformer unit, and a control circuit powered by said low voltage supply and responsive to said indication of the timing of the waveform of the ac supply to produce said control signal.
Preferably the control unit includes at least one manual control for varying said control signal to vary the conduction phase angle of the triac, and conveniently the control circuit comprises a microcontroller. For operation as a simple dawn simulator, the control circuit is responsive to initial application of said low voltage supply to produce said control signal to determine a relatively large conduction phase angle of the triac for supplying relatively little power to a load connected to the second connector of the transformer unit, and subsequently to produce said control signal to gradually decrease said conduction phase angle of the triac thereby to gradually increase power supplied to said load. A more sophisticated control unit can include a display controlled by the microcontroller to constitute a clock.
Another aspect of the invention provides a transformer unit comprising: a first connector comprising prongs extending from an enclosure of the transformer unit for insertion into an ac outlet to provide an ac supply to the transformer unit; a second connector forming an ac outlet in the enclosure of the transformer unit; a triac controlled via an opto-coupler, the first connector being coupled to the second connector via the triac to provide to the second connector an ac supply controlled by a control signal supplied to the opto-coupler; a transformer having primary and secondary windings, the primary winding being coupled to the first connector for receiving the ac supply; and a third connector comprising at least three wires for connection to a control unit separate from the transformer unit, said at least three wires providing said control signal from the control unit, a low voltage supply for the control unit derived from the secondary winding of the transformer, and an indication of the timing of a waveform of the ac supply.
The invention further provides a control unit for connection to such a transformer unit via the third connector of the transformer unit for providing said control signal to control a conduction phase angle of the triac in successive half cycles of the waveform of the ac supply, comprising a connector having at least three wires for coupling to the third connector of the transformer unit, and a control circuit including a microcontroller powered by said low voltage supply and responsive to said indication of the timing of the waveform of the ac supply to produce said control signal.
A further aspect of the invention provides apparatus comprising: a first connector for connection to an ac outlet to provide an ac supply; a second connector constituting an ac outlet; a triac, the first connector being coupled to the second connector via the triac to provide a controlled ac supply to the second connector; an electrically isolating coupler for coupling a control signal to the triac for controlling conduction of the triac; a transformer having primary and secondary windings, the primary winding being coupled to the first connector for receiving the ac supply; a rectifier and smoothing circuit coupled to the secondary winding of the transformer for providing a dc voltage; a zero crossing detector arranged to produce a zero crossing signal representing zero crossings of a waveform of the ac supply; and a control circuit powered by the dc voltage and responsive to the zero crossing signal to produce said control signal to control a conduction phase angle of the triac in successive half cycles of the waveform of the ac supply; wherein at least the first and second connectors, the triac, the electrically isolating coupler, and the transformer are provided in a transformer unit, and at least the control circuit is provided in a control unit separate from the transformer unit for electrical connection to the transformer unit via a third connector having at least three wires, the control unit and the third connector thereby being electrically isolated from the ac supply.
Conveniently in such apparatus the control circuit comprises a microcontroller and is arranged to produce said control signal to determine a conduction phase angle of the triac which is automatically and gradually decreased from a relatively large initial value to a smaller subsequent value, thereby to supply initially relatively little power and subsequently a gradually increasing power to a load connected to the second connector, and the control circuit also includes at least one manual control to which the microcontroller is responsive for determining said control signal to vary the conduction phase angle of the triac.
Thus the invention is directed to transformer and control units, individually and in combination, of which the control unit is properly isolated from an ac power supply to which the transformer unit can be connected, the transformer unit serving to supply low voltage power to the control unit and to supply ac power controlled by a triac to an ac outlet, the triac being controlled by the control unit.